The present invention relates to a device capable of inputting X, Y coordinates of a light emitting or absorbing stylus into a computer. Its design is such that the photo detectors used to determine the Cartesian coordinates of the stylus are used to digitize graphic information contained on sheet material such as paper.
Several techniques are known by which X and Y coordinates can be entered into a computer or other type system. Each has limitations which are avoided by the present invention.
The computer mouse system such as found in U.S. Pat. No. 4,464,652, and other patents, uses a hand-held device moved over a flat surface. X and Y movements of the mouse are converted into electronic signals transmitted to a computer. Generally, one or more buttons found on the mouse can be depressed to indicate desired actions. There are several characteristics of the mouse which may lessen its utility. First, the movement of the mouse occurs over a surface distinct from the screen of the computer. The user must, therefore, mentally translate the desired actions from the screen to the surface of the a desk. Second, the usual design of the mouse required that movements occur using gross arm movements rather than the precise movements of which the human hand is capable. This limits the accuracy of the X, Y coordinate indications. Third, some mouse designs require a special pad on which the mouse must move; all require necessary desk space in addition to the computer system for mouse movements. Calculating the total "footprint" (or required desk space) of the computer system must include, therefore, the necessary space for mouse movement. Fourth, mice designs generally require a connecting wire to the computer.
A second general technique used to enter X, Y coordinates into a computer system is the lightpen, for example U.S. Pat. No. 3,337,860. The lightpen in general is a hand-held wand having one or more photodetectors at one end. Placing the detector against the CRT screen of a computer display activates the photodetector when the raster spot passes under the detector. Timing circuits permit the determination of the coordinates of the lightpen. There are several limitations to the lightpen. First, for the lightpen to operate, it is necessary for the areas under the pen to be illuminated by the raster spot. Hence, it may be necessary to "flash" (light entirely) the screen to insure that the pen is not held to a dark, non-illuminated area. Second, because the lightpen works by timing when the section of screen it is held against is momentarily lit it follows that the nature of the phosphor used in the screen is an important parameter. Long persistence phosphors, which may be desirable to reduce flicker, can interfere with operation of the lightpen. Third, since there is a space between the inner surface of the CRT which is illuminated and the photodetector of the lightpen, parallax errors may occur. Fifth, light pens, too, generally require a connecting wire to the computer. Sixth, by their very design, lightpens work only be timing the illumination of small sections of CRT's or other displays whose screens are differentially lit at different times by a small illuminated spot. Light pens can not be used with flat screen displays which operate by other means.
A third method of entering X, Y coordinates, e.g. U.S. Pat. No. 4,205,304, is to use an opaque object, commonly a finger, to interrupt a rectangular grid of narrow light beams parallel to, and above, the CRT screen, focused on photodetectors at sides opposite from the light sources. Position is indicated by determining which beams in the X and Y direction are obstructed. This technique has the virtue of not requiring the user to manipulate a stylus or the device. One's finger is always at hand. One difficulty with previous designs is the necessity of directing the light from the light sources toward the photodetector. Several techniques have been used, for example complex circuitry to sequentially activate light sources, in order to ameliorate the problem of misalignment of light detector and light source. Another limitation to this technique is the requirement that there be a clear line of sight across the screen except for the obstructing finger or stylus. Thus, the user can not rest on the CRT or display screen any part of the hand such as the palm, heel or side in order to stabilize the finger for precise pointing.
Several patents have been issued for devices using light emitting styli to indicate Cartesian coordinates for computer input. The apparatus in U.S. Pat. No. 4,078,151 uses a plurality of photodetectors arrayed along the periphery of panel. As a light emitting stylus approaches any of the detectors, analog output from that detector increases. The position of the stylus is determined by the balance of analog outputs of photodetectors located on opposite sides of the pad. The present invention differs significantly from the apparatus in U.S. Pat. No. 4,078,151 in several respects. First, U.S. Pat. No. 4,078,151 requires a clear line of sight across the display surface, since it depends on a balance of analog outputs. Second, it is incapable of the detection of a light obstructing stylus such as a finger if desired. Third, it in incapable of resolving an image, and hence can not be used to digitize graphic material on a paper or the like.
U.S. Pat. Nos. 3,539,995, 3,618,029 and 3,673,579 use a pad consisting of a matrix of light detectors over which a light emitting stylus moves. It can easily be determined that to have a resolution of M by N units, it will be necessary to have M times N total detectors. For high resolution purposes, this can result in a very large number of detectors. Also, if the matrix of detectors is to be interspersed with a display screen, the mix of detectors and display elements will produce a undesirable granularity in both display and detection. Hereto, this technique also does not permit digitization of graphic material on paper or the like nor can it detect the position of opaque non-light emitting styli or fingers.
U.S. Pat. No. 4,550,250 also uses a light emitting stylus to indicate Cartesian coordinates for computer input. Inspection of U.S. Pat. No. 4,550,250 will clearly demonstrate significant differences between that invention and the one revealed here. U.S. Pat. No. 4,550,250 compares the analog output of a triangular or other shaped detector (whose analog output varies with the position of incident light) with that of a reference detector. The detectors of U.S. Pat. No. 4,550,250 can not digitize graphic information. Also, it would be impossible for the detectors of U.S. Pat. No. 4,550,250, to detect the position of an opaque light absorbing stylus or finger.
Many patents have been issued for the use of detectors to digitize graphic material on paper and the like, as well as associated logic for the recognition of character information contained thereon. For example, U.S. Pat. No. 4,292,621 reveals a device for character recognition which uses novel direction for the document movement. The difference between the invention revealed in this application and previous patents issued for the digitization of graphic information on paper and the like, as well as the body of knowledge generally know to artisans in this area, is in the use of photodetectors used otherwise to determine the position of a light emitting or absorbing stylus to also be used for the digitization of said graphic information.